An examination of the tissue interactions which cause embryonic lens formation is proposed. Our interest in the formation of the lens stems from the many experimental opportunities for studying inductive interactions leading to cell determination in this tissue. There is probably more information about inductive effects during lens ontogeny than in any other system for studying embryonic induction, except in the formation of the nervous system. We propose further studies, however, because new experimental information has led us to reevaluate the generally accepted models for these processes. While classic experiments argue that the optic vesicle is a major stimulus for lens formation in the ectoderm overlying it, our results suggest that this conclusion should be reexamined because of potential experimental artifacts, and we propose to do that here. Although experimental evidence has accumulated for the role of other tissues early in the lens induction process, these experiments do not adequately define the nature of these interactions, which is a second goal of our planned experiments. There is also extensive evidence that large regions of ectoderm in the embryo have the developmental potential to form a lens, and that this developmental potential is lost as embryogenesis proceeds. We have results arguing that this restriction of developmental potential results from an inhibitory interaction with underlying tissues, which we propose to characterize further. Our long range plan is to develop a coherent model for lens induction which will then permit us to examine intercellular signalling mechanisms which are important for lens formation and to establish whether specific modulations of gene expression lead to cell determination in this tissue.